RE: st: ST: postestimation test

Thanks Maarten this reply was helpful. I am now acquainted with "margins, post" and the subsequent use of test, as well as example #10, testing Margins, in the user guide entry for margins.
I have two followup questions.
First, if I understand the point about "test" only being available for model coefficients (or combinations), I am unsure what it was doing when I specified some combinations that were not estimated coefficients. For example:
. test 0.condition#0.ageGrp = 1.condition#1.ageGrp
( 1) [condCorr_pct]0b.condition#0b.ageGrp - [condCorr_pct]1.condition#1.ageGrp = 0
chi2( 1) = 1.38
Prob > chi2 = 0.2402
. test 0.condition#1.ageGrp = 1.condition#1.ageGrp
( 1) [condCorr_pct]0b.condition#1o.ageGrp - [condCorr_pct]1.condition#1.ageGrp = 0
chi2( 1) = 1.38
Prob > chi2 = 0.2402
In the 1st test, I compare the 11 interaction (which was a coefficient) to the 00 reference condition. Butin the 2nd test I tried to specify the 10 group to the 00 reference, and this was not a coefficient - yet it appeared to do something. Further what it did is identical to the result of the 1st test. What was Stata doing here?
Second, I am doing analyses for a colleague who writes for a literature where reporting mean differences, SDs, t/F stats, and p-values is the accepted practice. Is there some way to translate into t or F metric the chisq from the Wald test performed by the test command after I post the margins?
Also, can SE be sample size adjusted to yield SD with multilevel models? Would the number of level-2 groups be used as the sample size?
I know this is getting complex, but any further discussion or reference would be appreciated.
Thanks
-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Maarten buis
Sent: Friday, August 06, 2010 10:17 AM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: ST: postestimation test
--- On Fri, 6/8/10, Bontempo, Daniel E wrote:
> The model showed the interaction of two factors was
> significant, and I thought I could use "test" to probe
> which pairs of means were actually different. But some
> comparisons involving the reference condition do not
> work, and I am not sure why the test is giving chisq.
> -----
>
> . margins condition#ageGrp
<snip>
> . test 0.condition#1.ageGrp=1.condition#1.ageGrp
this test refers to the parameters in your model, not
to the table you get from margins. To test the differences
in predicted outcomes, you must first specify the -post-
option in -margins-.
-test- gives you a Chi square statistic because it
produces a Wald test of possibly multiple constraints, in
which case it cannot use the normal distribution as the
sampling distribution of the test statistic.
Hope this helps,
Maarten
--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany
http://www.maartenbuis.nl
--------------------------
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